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View Full Version : Engine/Deck/Deck Size Gearing Ratio questions & discussion


Envy Lawn Service
06-06-2005, 10:00 PM
OK, I've had my theories on this subject. But I wanted to question it and see what others theories are, ect.
Here's the example.....

OK, the 21hp Kawasaki is just OK on a 48" ZTR running side discharge.

The 23hp Kawasaki is strong on a 52" ZTR running side discharge.

The 21hp = 38.4 ft lbs of torque
The 23hp = 39.8 ft lbs or torque

Now... for me, it is hard to believe that 2hp and 1.4 ft lbs of torque accounts for everything in the difference felt.

Personally, as I have said before, I think the 48" deck is harder to pull than most think while still generating the same blade tip speed. The ratio between the PTO pulley and the spindle pulleys I believe is to blame. The spindle pulleys have to be smaller on the 48" in order for it to turn the shorter blades at the same tip speed. So the engine-to-deck gearing is higher to create the blade rpm's needed for the tip speed. So it is harder for the engine to turn under load, just like it would be hard to peddle a 10-speed bicycle up hill in a higher gear.

Does this make sense? Do you think I am right or wrong?

Also, is this also so much of a fact of the matter that you think the 21hp might feel closer to the 23hp if it were running the same 52" deck instead of the 48" deck? Or not?

Thanks for your thoughts.

dvmcmrhp52
06-06-2005, 10:05 PM
Horsepower and deck size along with deck design are factors to be reckoned with in my opinion.
Smaller decks don't move the clippings as well or as quickly as a larger deeper deck.

I'll give you an example.
A 23 horse Lazer HP with a 52" trivantage deck (5 " depth) will bog down and slow up before a 23 horse 60" decked Lazer with an ultracut deck (5 1/2 depth)
Both being Kohler motors, one being horizontal the other vertical.
Deck size and depth are important factors.

Envy Lawn Service
06-06-2005, 11:01 PM
Horsepower and deck size along with deck design are factors to be reckoned with in my opinion.
Smaller decks don't move the clippings as well or as quickly as a larger deeper deck.

I'll give you an example.
A 23 horse Lazer HP with a 52" trivantage deck (5 " depth) will bog down and slow up before a 23 horse 60" decked Lazer with an ultracut deck (5 1/2 depth)
Both being Kohler motors, one being horizontal the other vertical.
Deck size and depth are important factors.

Very true statement there. I didn't know that was true of the 23/60 Lazer Z though. That's cool to know. Learned something new today! Anyways, that 23/60 Lazer Z must not be shabby at all then as I would have thought.

Here is a second fact back at you. Until what you said, I did not buy into the "kawasaki feels stronger because of more torque at the same hp" statement. Not at all. But I have to say, you should really see how 'strong' the 23hp Kawasaki is in the HP application. You can barely make it labor at speed, even in 2 weeks growth. What I really mean by that is that speed will effect cut quality before you can really bog the engine down enough to hear. But she DRINKS gas.

Anyways, I'm getting off topic a hair there. So back on in relation to what you said.... Of the two compaired in my example, both were V-shaft with very similar setups. The decks also have about the same basic shell design and depth. But the 21hp was coupled with a more open, free flowing deck than the 52" which was one factor I thought would help the 21hp feel a bit better. But it doesn't. The two feel a world apart, despite the fact they share the same block and the 23hp is pulling a larger deck with tighter baffling.

dvmcmrhp52
06-07-2005, 12:06 AM
Very true statement there. I didn't know that was true of the 23/60 Lazer Z though. That's cool to know. Learned something new today! Anyways, that 23/60 Lazer Z must not be shabby at all then as I would have thought.

Here is a second fact back at you. Until what you said, I did not buy into the "kawasaki feels stronger because of more torque at the same hp" statement. Not at all. But I have to say, you should really see how 'strong' the 23hp Kawasaki is in the HP application. You can barely make it labor at speed, even in 2 weeks growth. What I really mean by that is that speed will effect cut quality before you can really bog the engine down enough to hear. But she DRINKS gas.

Anyways, I'm getting off topic a hair there. So back on in relation to what you said.... Of the two compaired in my example, both were V-shaft with very similar setups. The decks also have about the same basic shell design and depth. But the 21hp was coupled with a more open, free flowing deck than the 52" which was one factor I thought would help the 21hp feel a bit better. But it doesn't. The two feel a world apart, despite the fact they share the same block and the 23hp is pulling a larger deck with tighter baffling.



I'll go back to deck size..............
The 48" deck just doesn't have the capacity to remove debris (in volume) as quickly as the 52" deck. The tighter baffling or discharge chute increases the speed at which the clippings are thrown from the deck but the volume that can be handled inside the deck is still greater on the 52 versus the 48.

Making any sense...........Maybe?

Envy Lawn Service
06-07-2005, 12:12 AM
Yeah, I can understand that concept too.
Greater volume of space under the 52" deck v/s a 48" deck of the same MFG.

Tonyr
06-07-2005, 12:21 AM
geeeeeeezzzzz, mate, you got any Easy questions? :help:

It's only early in the week ya know! HA HA :cool2:

dvmcmrhp52
06-07-2005, 12:28 AM
Keep in mind as well, each model and engine/deck combo
can be running at different rpm's on the engine.
Engine rpm on the Lazer XS is different than the Lazer and Lazer HP.
There are many variables involved and even one machine to the next can vary a bit in ground speed, tip speed, rpm's, etc.

Add them all together and things seem to change............
We've got an HP that has a faster ground speed than the standard Lazer.............Why? Never spent the time to find out.

One other thing............
The 23 horse lazer 60" will outdo a 23 horse Lazer HP 52" in heavy cutting conditions while also carrying more machine weight and pulling more tire friction because of wider tires..................Hmmmmm...............

dvmcmrhp52
06-07-2005, 12:29 AM
geeeeeeezzzzz, mate, you got any Easy questions? :help:

It's only early in the week ya know! HA HA :cool2:






G'day ya old codger!
Good ta see ya...............

Envy Lawn Service
06-07-2005, 01:41 AM
dvmcmrhp52,

Thanks, your extra input is turning this into a good thread. I think this is a great subject to explore. It's a good 'thought process' type of thread on the specifics of how stuff actually works instead of the 'norm' type of thread we see on here all the time about equipment....

dvmcmrhp52
06-07-2005, 07:10 PM
I'd like to hear comparisons with 72" decks.................